Effects of Span on Local Scour Depth around Four Columns of Tandem Piers in Clear Water

Qi, Hongliang; Zhang, Chenguang; Xuan, Weilin; Tian, Wei; Li, Jiachun

doi:10.1007/s40996-023-01106-w

Cited by 2 publications

(2 citation statements)

References 37 publications

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“…The upstream pillar influences the scouring of the downstream pillar through two mechanisms: firstly, by modifying the flow patterns of vortex areas that serve as the incoming flows for scouring the downstream pillar; the second mechanism involves sediment scoured by the upstream pillar being transported to the scour hole of the downstream pillar, leading to the scour depth of downstream pillar generally being less than that of the upstream pillar [63,64]. Additionally, at different spacings between adjacent pillars, the scour depth at the upstream pillar remains almost the same as that of a single pillar, while the scour depth at the downstream pillar increases with the diameter and spacing of the pillars [65,66]. Furthermore, when the water flow approaches the downstream pillar, a recirculation zone forms between adjacent pillars near the bed, causing flow reversal and drawing more bed sediment that is subsequently carried downstream [64].…”

Section: Wind Turbines Induce Change In Local Tidal Currentmentioning

confidence: 99%

Study on the Impact of Offshore Wind Farms on Surrounding Water Environment in the Yangtze Estuary Based on Remote Sensing

Cai,

Hu,

Qiu

et al. 2023

Remote Sensing

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Offshore wind farms (OWFs), built extensively in recent years, induce changes in the surrounding water environment. The changes in the suspended sediment concentration (SSC) and chlorophyll-a concentration (Chl-aC) induced by an OWF in the Yangtze River Estuary were analyzed based on Chinese Gaofen (GF) satellite data. The results show the following: (1) The flow near the wind turbines makes the bottom water surge, driving the sediment to “re-suspend” and be lost, deepening the scour pit around the bottom of the wind turbines, which is known as “self-digging”. The interaction between the pillar of a wind turbine and tidal currents makes hydrodynamic factors more complicated. Blocking by wind turbines promoting the scour of the bottom seabed of the OWF results in speeding up the circulation rate of sediment loss and “re-suspension”, which contributes to the change in the SSC and Chl-aC. This kind of change in sediment transport in estuarine areas due to human construction affects the balance of the ecological environment. Long-term sediment loss around wind turbines also influences the safety of wind turbines. (2) The SSC and Chl-aC are mainly in the range of 200–600 mg/L and 3–7 μg/L, respectively, in the OWF area, higher than the values obtained in surrounding waters. The SSC and Chl-aC downstream of the OWF are higher than those upstream, with differences of 100–300 mg/L and 0.5–2 μg/L. High SSC and Chl-aC “tails” appear downstream of wind turbines, consistent with the direction of local tidal currents, with lengths in the range of 2–4 km. In addition, the water environment in the vicinity of a wind turbine array, with a roughly 2–5 km scope (within 4 km during flooding and around 2.5 km during ebbing approximately) downstream of the wind turbine array, is impacted by the OWF. (3) In order to solve the problem of “self-digging” induced by OWFs, it is suggested that the distance between two wind turbines should be controlled within 2–3.5 km in the main flow direction, promising that the second row of wind turbines will be placed on the suspended sediment deposition belt induced by the first row. In this way, the problems of ecosystem imbalance and tidal current structure change caused by sediment loss because of local scouring can be reduced. Furthermore, mutual compensation between wind turbines can solve the “self-digging” problem to a certain extent and ensure the safety of OWFs.

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Section: Wind Turbines Induce Change In Local Tidal Currentmentioning

confidence: 99%

Study on the Impact of Offshore Wind Farms on Surrounding Water Environment in the Yangtze Estuary Based on Remote Sensing

Cai,

Hu,

Qiu

et al. 2023

Remote Sensing

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“…There are also many results for local scour behavior around multiple piers. Qi et al [24] studied the effects of span on local scour depth around four columns of tandem piers in clear water. The study showed that when the span is smaller than 30.0D, local scour depths around other piers in each column decrease along the flow direction gradually and eventually become stable.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study on Local Scour Reduction around Two Cylindrical Piers Arranged in Tandem Using Collars

Qi,

Yuan,

Zou

et al. 2023

Water

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Local scour occurring near bridge piers has become a major problem all over the world, which has caused countless bridge damage events. Explorations regarding local scour reduction measurements have become a research hotspot in the field. Much effective research has been conducted on scour reduction for single piers. However, studies on local scour reduction around multiple piers that are arranged in tandem have rarely been reported. Therefore, the effect of the span and the local scour reduction measurement (collar) on the characteristics of the local scouring behavior around two piers arranged in tandem are explored in this research, with numerical simulations in clear-water conditions. The results show that the local scour depth of the downstream pier increases gradually with an increase in the pier spacing, due to the weakened sheltering effect of the upstream pier. The local scouring of both the upstream and downstream piers can be reduced if the upstream pier is protected by a collar. The local scour reduction efficiency of the upstream pier can reach 52~55%. The local scour reduction efficiency of the downstream pier decreases rapidly from 84.3% to 8.3% with an increase in the pier spacing. If the pier spacing, G, is greater than 4.0D (D is the diameter of the pier), the local scour depth around the downstream pier is larger than that around the upstream pier. Therefore, if the local scour depth of the upstream pier is considered safe and acceptable, it is used as the reduction target of the downstream local scour depth. A collar must be adapted for use around the downstream pier when G/D > 4.0. If both the piers are protected by collars of the same size (W = 3.0D), the local scour reduction efficiency of the downstream pier is about 15% more than that of the upstream pier. The local scour depth around the downstream pier is 64.5% of that around the upstream pier. Therefore, the size of the collar around the downstream pier can be decreased to save costs. The local scour reduction efficiency for the downstream pier reduces from 66.7% to 39.8% when the downstream collar size (W) decreases from 3.0D to 2.0D. To ensure that the local scour depth around the downstream pier is no greater than that of the upstream pier, the downstream collar should be larger than 2.25D. These results can serve as a reference for the local scour reduction of two piers arranged in tandem.

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Effects of Span on Local Scour Depth around Four Columns of Tandem Piers in Clear Water

Cited by 2 publications

References 37 publications

Study on the Impact of Offshore Wind Farms on Surrounding Water Environment in the Yangtze Estuary Based on Remote Sensing

Study on the Impact of Offshore Wind Farms on Surrounding Water Environment in the Yangtze Estuary Based on Remote Sensing

Numerical Study on Local Scour Reduction around Two Cylindrical Piers Arranged in Tandem Using Collars

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